Effects of Biocide Concentration on Calcium Carbonate Slurries

1
Effects of Biocide Concentration on Calcium
Carbonate Slurries
Introduction The aim of this project was to
develop a biological assay to determine the
amount of available biocide contained within
treated samples of calcium carbonate slurries.
The slurries are used in the production of paper
and contamination with micro-organisms can occur
at any time during the storage and transport of
the slurries. Bacterial growth can cause pH
changes, leading to discolouration, unpleasant
odours and an increase in the viscosity of the
slurries which can lead to problems during
processing, as well as adversely affecting the
quality of the final product. For these reasons
the use of biocides is essential for maintaining
the purity of white mineral dispersions and
optimising their efficiency is essential not only
for cost implications but also to minimise the
development of resistance and to comply with EU
regulations.
Method The Cellfacts II enables real time
analysis of samples, allowing cell populations to
be detected, sized and counted. Using staining
methods with a fluorescent dye the viability of
the cells can be determined by the electrical
potential of the cell membrane. Both a time
assay and a biocide assay were carried out on
three isolates obtained from calcium carbonate
slurry samples. A micro titre tray was used to
prepare the samples as shown by the diagram on
the right. The samples were then stained and then
run through the Cellfacts II machine. The
remaining solution left in the wells was used to
plate out 3 spots for each dilution and each time
or concentration of biocide used, to perform
colony counts the next day.
Results
Figure 1 Growth profile of isolate FT11 treated
with biocide BK14 over 0-90min
Figure 2 Biocide assay of slurry contaminant
FT11
Figure 3 Effect of biocide BK14 concentration on
isolate FT11
Cells without biocide (90min)
Cell lysis after 60min
Cell elongation
FT11 (0min) FT11 (60min) FT11 (90min) FT11
control
31ppm 62ppm 125ppm 250ppm 500ppm control
Fluorescence values Cell count
At a concentration of 62ppm of biocide BK14,
total cell lysis can be seen as there is a
dramatic decrease in cell number.
There is a significant drop in mean fluorescence
values as the cell numbers start to decline.
After 60minutes contact time with the biocide,
inhibition of cell growth can be seen and
compared to the positive control, cell elongation
occurs after 90min.
Conclusions The results indicate that low
concentrations of biocide BK14 are needed to
achieve an inhibitory effect on the slurry
contaminants examined in this experiment. The
consequences of treatment included cell lysis,
cell shrinkage and a substantial decrease in
fluorescence values which equates to a decrease
in viability. For future experiments, more
investigations into the lower spectrum of biocide
concentrations would be needed to obtain a
clearer profile of what is actually happening to
the cells following treatment.
The URSS Experience The experience has enabled me
to gain confidence and experience in working on a
research project. Using practical skills and
using new pieces of equipment being responsible
for the organisation of materials required to
carry out the experiments and also gaining
knowledge in interpreting the data obtained. Time
management and prioritising activities was also a
major factor.
Vicky Bateman 2nd year undergraduate student
Acknowledgements Dr.Crawford Dow and Dr.Uthaya
Swoboda